In underground metal mines that use sublevel or stage open-stope and backfilling mining methods (SSOBMMs), there is a special structure around which both sides of the rock pillar are wrapped by backfill. As a permanent part of an underground mine, how much can backfill improve the rock pillar’s compressive strength? What is the difference in the mechanical properties between the special structure and the signal rock? To explore these questions, a composite structure made of a cement-tailing backfill (CTB) and rock core (RC) was designed. Uniaxial and triaxial compressive strength tests and scanning electron microscope (SEM) were used to research the mechanical properties, failure process, failure characteristics, and microstructure characteristics of the cement-tailing backfill and rock core (CTB-RC) specimens. It was found that the full stress–strain curve of the CTB-RC specimen under triaxial compressive strength (TCS) test had two times the stress increases reaching a lower peak deviator stress two times after the RC was destroyed. The CTB can reduce the destruction and slow down the deformation speed of the inner rock cor (IRC). It can also prevent rigid slip of the IRC after it is damaged and maintain the stability and integrity of the overall structure. The findings of this study can provide some basic knowledge on the mechanical properties of the CTB-RB and provide theoretical guidance for the optimization direction of the width of the rock pillar and the room in mines using SSOBMMs.

Aiming to solve the problems related to the slow settling speed and the long-term consumption of ultra-fine tailings in mine filling, the effect of flocculant type on the flocculation and settling performance of ultra-fine tailings was studied through static sedimentation experiments on tailings. The microstructure of the flocculation was observed and analyzed using an electron microscope. On this basis, the selection of the optimum flocculant type and dosage parameters was carried out. The results show that the best addition amount of the AZ9020 anionic flocculant was 30 g/t, a solution concentration of 0.3%, and a stirring time of more than 45 min. The floc structure of the full-tailings flocculation solution was formed by the AZ9020 anionic flocculant. Moreover, the size of less than 0.1 μm was still relatively large; thus, the overall size of the structure was small and uniformly dispersed. The floc solution had the smallest porosity, the fractal dimension was the largest, the molecular weight of the floc was the largest, and the floc was the most compact, making it appropriate for the rapid removal of floc structures from water. Sedimentation is also the best flocculant for flocculation and sedimentation. The size of the flocs decreased as the height of the flocculation sediment bed increased during flocculation and sedimentation. The research results provide a microscopic view for the selection of the best flocculant type.

This study analyzes the stability and optimizes the parameters of the bottom structure in sublevel stoping with the delayed backfilling method, improves production efficiency, and increases the ore recovery ratio under the premise of ensuring safe production. Theoretical formulas are used to calculate the stability of the pillar with the bottom structure. Numerical simulation is used to study the stability of muck slash during excavation. Finally, the optimization parameters of the bottom structure are obtained by combining a similar physical experimental model and numerical simulation. The results show that the excavation of the muck slash caused different degrees of deformation at the roof and floor of the roadway. The largest stress occurred at the roadway crossing, whereas the smallest stress was in the middle area. The excavation also caused the secondary stress concentration at the adjacent bottom structure but did not significantly impact its stability. During the mining process, the largest displacement deformation occurred at the roadway crossing, and the influence of mining disturbance on the stability of the bottom structure involves timeliness and periodicity. Considering the recovery ratio, dilution ratio, and stability, the spacing of the extracted ore drift is recommended to be 9 m. This study ensures the stability of the bottom structure in the mining process and obtained reasonable parameters of the extracted ore drift, which provides a scientific way for the mines that use sublevel stoping with the delayed backfilling method.

To explore the hydration characteristics and early strength evolution of classified fine tailings cemented backfill (CFTCB), a nuclear magnetic resonance (NMR) analysis and a volume resistivity test were performed on classified fine tailings filling slurry (CFTFS). The early hydration products of CFTCB were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD) phase analysis. Uniaxial compressive strength (UCS) test was carried out, and the microscopic characteristics and strength rules of the hydration reaction of CFTCB were analyzed. Based on the experiment, we found the law of water content change and porosity evolution. The early hydration reaction can be divided into the dissolution, setting, and hardening stages. The volume resistivity test results show that the volume resistance of filling slurry increases slowly at first then decreases, and finally increases rapidly. The variation trend of volume resistivity is related to the degree of hydration reaction. When combined with the hydration characteristics of backfill materials, the hydration reaction rate determines the growth rate of early strength of backfill, and the formation of hydration products is the reason for the early strength increase in backfill. The research conclusion has an important theoretical guiding value and engineering significance in mine filling production organization and filling ratio parameter optimization.